In addition to pure polyamides and polyesters from aliphatic or aliphatic/aromatic components for the production of fibers and molded articles, also polyester amides have been described. In addition to copolymers of polyethylene terephthalate and polyamide 6 (J. Polym. Sci. Part B: Polym. Phys. 26 (1988) 7, 1469-81). Polyesters from aromatic diacids, hydroxycarboxylic acids, diols, aminocarboxylic acids, aminophenols and diamines have been disclosed for this purpose (U.S. Pat. Nos. 3,272,774; 4,272,625; 4,351,918; and 4,355,132; European patent No. 0 067 032; Japanese patents Nos. 61-236826; 61-236827; and 61-239014). These fully aromatic polyester amides have, because of their structure, outstanding properties, such as a high tensile strength and high resistance to thermal deformation. The presence of amide bonds and the aromatic components in the polymer result in an increase in the crystallinity and the melting temperature.
Temperatures in excess of 300.degree. C. and, in some cases, in excess of 400.degree. C. are therefore required for production and processing (spinning, injection molding, film extrusion). At these temperatures, however, decomposition reactions may already occur.
Polyester amides, which permit lower production and processing temperatures (as described e.g. in U.S. Pat. No. 4,182,842) include of polyethylene terephthalate and paraaminobenzoic acid. The molecular weight of this polyester amide after a 4-hour condensation is still too low for the processing of high-strength molded articles. For this reason, to increase the molecular weight, the polyester amide has to be subjected after the melt condensation to several hours (approximately 13 hours) of an energy-consuming solid phase condensation.
Moreover, copolyester amides are described, in U.S. Pat. No. 4,839,128, of ethylene glycol, aromatic diacids, aromatic diols, other aromatic diacids, aromatic hydroxycarboxylic acids, aromatic diamines, aminophenols and aminocarboxylic acids. The desired properties of the polyester amide are achieved according to this reference only by incorporating two other monomers, namely an aromatic diol and a further aromatic diacid, in addition to the polyester building blocks of ethylene glycol, aromatic diacid, hydroxybenzoic acid, and amide-forming monomers (diamine, aminophenol, aminocarboxylic acid). However, in melt condensation, the incorporation of such additional comonomers can lead to the formation of block structures in the polymer chain, which adversely affect the properties of the polymer.
Various methods are known for the production of polyester amides. Frequently, dicarboxylic acids, acetylated diamines, acetylated hydroxycarboxylic acids and acetylated diamines, aminophenols and aminocarboxylic acids are condensed by a transesterification/transamidation reaction in the melt to form polyester amides, with a low boiling carboxylic acid being formed as volatile condensate (Japanese patent Nos. 61-236826; 61-236827; and 61-239014; European patent No. 0 067 032; U.S. Pat. Nos. 4,182,842; 4,272,625; and 4,839,128. In addition to the requirement of a 4-hour melt condensation, this method for preparing polyester amides with aliphatic diol units, next also requires several hours of solid-phase condensation (U.S. Pat. No. 4,182,842), to obtain polycondensates of sufficiently high molecular weight.
A different method as described in GDR patent No. 271,823, discloses the reaction of polyalkylene-arylene dicarboxylate esters with aromatic diamines to produce polyester amides, while alkylene diol is liberated as the volatile condensate. The free diamines, used for this reaction can easily be oxidized. The resulting polyester amides therefore frequently have a dark color.
A further method synthesises polyester amides from dicarboxylic acid chlorides, diols, diamines and aminophenols. The reaction, however, releases corrosive hydrogen chloride gas, which must be bound by bases. In addition, the reaction must be carried out in solvents (dimethylformamide, etc.). For this reason, an expensive solvent recovery process is necessary (J. Polym. Sci., Polym. Chem. Ed. 22 (1984) 12 3983-3988; J. Polym. Sci., Polym. Chem. Ed., 19 (1981) 3285 ff.).
The linking of linear polyesters with diisocyanates for the production of polyurethanes or unsaturated polyester resins is well known (Plaste und Kautschuk, 15 (1968), 347). The reaction involves the formation of urethane bonds, which are no longer stable at the synthesis and processing temperatures employed for highly aromatic/aliphatic copolyesters. The thermal decomposition temperature for urethanes from aromatic isocyanates and R--OH is about 200.degree. C. when R is aliphatic and about 130.degree. C. when R is aromatic (Polyurethane, Fachbuchverlag Publisher, Leipzig, 1973, page 24).
It is furthermore well known that isocyanates tend to form the corresponding trimers at high temperatures and in the presence of basic catalysts, such as alkali acetates (Ullmans Encykl. tech. Chem., 1957, vol. 9, page 4, and Kunststoffhandbuch (Plastics Handbook) vol. 7, Polyurethanes, page 81). The trivalent isocyanurates, formed from diisocyanates, have three reactive NCO groups. When these react with linear copolyesters, they can cause branching and/or crosslinking in the polyester amide. Alkali acetates and many other metal acetates are known as conventional transesterification catalysts and are therefore practically always contained in polyesters and copolyesters, particularly in polymers, which are produced by the transacylation reactions with the splitting off of acetic acid (Polyesterfasern (Polyester Fibers), 1975, Akademieverlag Berlin, pages 116-117). Branched and crosslinked polymers have higher melting points and lower solubilities than the corresponding polymers, which are not branched or crosslinked. They may even be infusible. These polymers can therefore be processed by thermoplastic means only with difficulty, if at all.